Re: Freezing without write I/O

On Fri, 2013-08-30 at 20:34 +0200, Andres Freund wrote:
> I have a quick question: The reason I'd asked about the status of the
> patch was that I was thinking about the state of the "forensic freezing"
> patch. After a quick look at your proposal, we still need to freeze in
> some situations (old & new data on the same page basically), so I'd say
> it still makes sense to apply the forensic freezing patch, right?
>
> Differing Opinions?

The Freeze Forensically patch is nice because (if I understand it
correctly) it allows us to freeze at the same time as we mark
PD_ALL_VISIBLE, which avoids the potential extra page write. But that's
not such a big advantage if we don't ordinarily have to write again for
freezing, anyway.

However, there are still some cases where we'd be able to preserve the
forensic information. If nothing else, that might help debug this patch,
if necessary. There might also be cases where we can freeze more eagerly
to avoid the case where very old (but unfrozen) and very new tuples mix
on the same page. Perhaps Robert has some thoughts here, as well.

Regards,
Jeff Davis